1. Field of the Invention
The invention relates to an abnormality detection apparatus and an abnormality detection method for a Rankine cycle system in which waste heat produced by an internal combustion engine is recovered via vapor.
2. Description of Related Art
A waste heat recovery apparatus that recovers waste heat produced in connection with the driving of an internal combustion engine by using the Rankine cycle is known. In a waste heat recovery apparatus of this kind, a water-cooled cooling system of an internal combustion engine is constructed so as to have a sealed structure, and an expander (turbine) is driven by using a cooling medium (vapor) vaporized by waste heat of the internal combustion engine, and thermal energy that the vapor has is recovered by converting it into mechanical power or electric energy. For example, a waste heat recovery apparatus described in Japanese Patent Application Publication No. 2008-169760 (JP-A-2008-169760) converts thermal energy into electric energy by supplying the coolant from the engine to a superheater via a gas-liquid separator so that the coolant vaporizes, and then actuating the expander through the use of the generated vapor.
Besides, apparatuses that determine the presence or absence of failure of such a waste heat recovery apparatus have been disclosed as mentioned below. A waste heat recovery apparatus described in Japanese Patent Application Publication No. 2010-174848 (JP-A-2010-174848) determines whether a cooling medium pump has failure by monitoring the pressure in a circuit of the Rankine cycle by using a cooling medium pressure sensor that is provided in a flow path between a cooling medium pump and an evaporator. A heat cycle apparatus described in Japanese Patent Application Publication No. 2006-17108 (JP-A-2006-17108) determines whether the Rankine cycle has abnormality by comparing a difference value between an upstream pressure value and a downstream pressure value of a liquid pump with a predetermined pressure value. A cooling apparatus for an engine described in Japanese Patent Application Publication No. 2009-79505 (JP-A-2009-79505) determines that an electric water pump has a failure if at the elapse of more than a predetermined time after the electric water pump is activated, the liquid surface level in the water jacket has not reached a liquid surface level that is expected to be reached on the basis of the amount of the coolant pumped by the electric water pump while a coolant is supplied from a thermal storage tank into a water jacket, and determines that there is clogging of an electromagnetic valve or of a coolant passageway if at the time of discharging the coolant from the water jacket into the thermal storage tank, the liquid surface level in the water jacket is not declining.
By the way, in a Rankine cycle system that recovers waste heat of an internal combustion engine, waste heat from the internal combustion engine cannot be recovered if the cooling medium or vapor that is a working fluid does not circulate normally in the Rankine cycle system. When the working fluid does not circulate normally in the Rankine cycle system, various causes are conceivable, including a failure of a cooling system of the internal combustion engine, a failure of an electromagnetic valve or a water pump disposed in a passageway through which the working fluid circulates, a leak of the working fluid between passageways, etc. Therefore, in order to specifically determine the cause of the working fluid failing to circulate normally in the Rankine cycle system, it cannot be said to be sufficient to merely perform a determination regarding a single cause. That is, it is necessary to synthetically perform determination regarding events that can be causes of the failure in the normal circulation of the working fluid in the Rankine cycle. However, although there have been disclosed apparatuses that perform determination regarding individual causes of the failure in the normal circulation of the working fluid in the Rankine cycle system, a construction that synthetically performs determination regarding such causes has not been disclosed. Hence, the Rankine cycle system still has room for betterment.